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The act of combining elements of a set.
Multiplying, dividing, adding and subtracting are specific operations used on the set of numbers. Two numbers can be combined using one of these operations to produce a third number.
Using the numbers 8 and 2:
multiplying them produces 16;
dividing them produces 4(or a quarter);
adding them produces 10;
while subtracting them produces 6 (or -6, negative six).
The order of doing operations on numbers is very important.

A kind of function, like addition, multiplication, etc, which takes in one or more input arguments, and produces a single number as an answer.

On a set: an n -ary function.
See also closed, sense 3.